Stationary induction apparatus having sound attenuating means



March 29, 196 L. R. TOOTHMAN ETAL STATIONARY INDUCTION APPARATUS HAVINGSOUND ATTENUATING MEANS Filed Feb. 27, 1962 2 Sheets-Sheet 1 March 29,1966 R. TQOTHMAN ETAL 3.2439747 STATIONARY INDUCTION APPARATUS HAVINGSOUND ATTENUATING' MEANS Filed Feb. 27, 1962 2 Sheets-Sheet" 2/IIIIInu/l/A cgzzgi l-TT Q Q I" .ml f

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ATTURA/EY United States Patent 3,243,747 STATIONARY INDUCTION APPARATUSHAVING SOUND ATTENUATING MEANS Lawrence RfToothman and ArnoldL..Horelick, Bridgeville, Pa., as'signors to McGraw-Edison Company,Mllwaukee, Wis., a corporation of Delaware Filed Feb. 27, 1962, Ser. N0.17 6,082 12 Claims. (Cl. 336--100) This invent-ion relates to means forreducing audible Sound propagated by encased vibratory force generatingapparaths and more particularly to means for reducing audible soundgenerated by encased stationary induction apparatus.

Vibratory force generating electrical apparatus which produce audiblesound are often immersed in a dielectric liquid within a metalliccasing. Usually the force generatorrests upon the bottom wall' of thecasing, and often a rigid base of longitudinal and transverse structuraliron members is positioned below and aflixed to the casing bottom wallto facilitate handling and to support the weight of the liquiddielectric and the electrical apparatus. The vibration-s generated bythe sound propagating apparatus rriay excite the rigid base structure todifferent amplitudes of vibration. The casing side walls areconventionally rigidly connected to the base structure, and thevibrations of the stiff basemembersmay force the casing side walls intovibration and result in a high noise level.

It is well know that the magnetic core is a source of sound in anelectrical transformer. Energization of the electrical windingssurrounding the legs of the magnetic core results in alternatingmagnetization of the core, and the core laminations cyclically expandand contract due to the phenomenon of magnetostriction when magnetizedand demagnetized'by the current flowing in the transformer windings. Themagnetic core thus acts as a source of 120 cycle vibrations andharmonics thereof. The vibrations generated by the magnetic coretogether .with theweight of the core and coil assembly may force therigid base structure beneath the casing bottom wall into vibration. VThe casing side walls are rigidly connected to the base structure andmay be driven into vibration by the stiff base members and propagateaudible noise. When the rigid base structure is resonant at 120 cyclesor a harmonic thereof, the propagated noise level may be even morepronounced.

Electrical transformers are known wherein the core and coil areresiliently supported upon springs to mechanically decouple the sourceof sound from the casing, for example, the construction disclosed in thecopending application of Morton M. Aronsonet al., Serial No. 130,920filed August 11, 1961, now US Patent 3,125,736, and having the sameassignee as this application. Although such spring suspension of thetransformer core and coil assembly is effective in eliminating thedirect metallic coupling between the source of sound and the casing, ithas little or in influence on the coupling between the magnetic core andthe casing established through the substantially incompressible liquiddielectric. The coupling through the liquid dielectric is comparable tothe direct mechanical coupling in its ability to transmit vibrations andit forces a larger area of the casing bottom wall into vibration.

It is an object. of the invention to provide an encased vibratory forcegenerating apparatus supported on a rigid base structure wherein thebase structure is acoustically isolated from the sound propagatingsource.

It is a further object of the invention to provide encased, liquidimmersed, stationary induction apparatus supported on a rigid basestructure wherein both the direct metal coupling and the couplingthrough the liquid Patented Mar. 29, 1966 between the apparatus and thebase structure is minimized.

Another object of the invention is to provide encased, oil-immersed,stationary induction apparatus supported on a rigid base structurewherein the direct metal coupling and the coupling through the liquidbetween the core and coil assembly and the base structure are reduced toa level substantially below that between the core and coil assembly andthe casing side walls.

Another object of the invention is to provide encased stationaryinduction apparatus wherein the casing is integral with but isacoustically decoupled from the rigid base structure.

Another object of the invention is to provide encased stationaryinduction apparatus wherein the casing bottom wall is resilientlysupported out of contact with the rigid base structure so that it canvibrate as a diaphragm and a hollow chamber is provided between thecasing and the base structure wherein said casing bottom wall canvibrate as a diaphragm to attenuate vibratory energy and which enclosesthe resilient supporting means and seals them from the atmosphere. I

A still further object of the invention is to provide encased stationaryinduction apparatus wherein the casing bottom wall is resilientlysupported out of contact with the rigid base structure and having meansfor forming a hollow chamber between the casing and base structurewherein said casing bottom wall can vibrate as a diaphragm to attenuatevibratory energy and which integrally unites the casing to the basestructure without appreciable acoustic coupling therebetween.

In accordance with the invention the bottom wall of the casing is madeequal in thickness or thinner than the casing side walls and isresilently supported out of direct contact with the rigid base structureso the casing bottom wall can vibrate as a panel and does not possessthe stiffness necessary to force the casing side walls into vibration.

The features of this invention which are believed to be novel are setforth with particularity in the appended claims. The invention itself,however, both as to its organization and use, together with furtherobjects and advantages thereof, may best be understood by reference tothe following description taken in connection with the accompanyingdrawing in which FIG. 1 is a vertical section view through a preferredembodiment of the invention; FIG. 2 is a sectional view taken along line22 of FIG. 1; FIG. 3 is a horizontal view taken along line 3--3 of FIG.1; FIG. 4 is a partial sectional view through an alternative embodimentof the invention; and FIG. 5 is a partial view in perspective showing apreferred form of isolating pad means.

Referring now to FIGS. 1-3, the invention will be described withreference to an electrical power transformer having a three leggedmagnetic core 10 of magnetic steel laminations 1 1 defining threealigned verticalwinding legs 12 connected by upper and lower yokes 14and 15 respectively. Each winding leg 12 is surrounded by a cylindricalelectrical winding .17. Channel ir'on side frame members 18 are disposedon opposite sides of and afiixed by bolts 19 to the upper core yoke 14and to the lower core yoke 15.

The magnetic core 10 and the windings 17 comprise a transformer core andcoil assembly 20 contained within a metallic casing, or tank 21. Aliquid dielectric such as transformer oil 22 fills the casing 21 to alevel 23 above the core and coil assembly 20. A cushion of suitabledielectric gas 25 fills the casing 21 above the oil 22. The tank 21'includes a bottom wall 27 afiixed to pairs of opposed side walls 28 andis hermetically sealed by a cover 29. For reasons to be discussedhereinafter, the casing bottom wall 27 is equal in thickness or thinnerthan the tank side walls 28, and in the preferred embodiment the bottomwall 27 extends beyond the side walls 28 in a peripheral flange 31.Electrical connections to the windings 17 within casing 21 may be madethrough insulating bushings 32 mounted on and extending through thecover 29.

The core and coil assembly 20 is supported on a plurality of core feet33, which may be inverted channel iron members, transverse to anddisposed below the lower side frame members 18 and preferably aflixedthereto by suitable means such as welding. The core feet 33 aresymmetrically arranged relative to the center of gravity of the core andcoil assembly 20 and preferably are disposed below the winding legs 12where the weight of the core and coil assembly 20 is concentrated.

A rigid base structure 34 beneath the tank 21 comprises stiif channeliron members 36 longitudinal of the tank secured preferably by weldingto stiff channel iron members 37 transverse of the longitudinal members36. The longitudinal members 36 and transverse members 37 are preferablyarranged symmetrically relative to the center of gravity of the core andcoil assembly 20 and the tank 21, and in the embodiment of FIGS. 1-3 thetransverse members 37 are disposed approximately in vertical alignmentwith the outer core legs 12 and outer core feet 33 and the longitudinalmembers 37 are positioned approximately below the casing side walls 28longitudinal of the casing 21. In this embodiment a stiff top plate 39is disposed above and rigidly aflixed by welding to the crossedstructural iron members 36 and 37. The top plate 39 is substantiallycoextensive with the casing bottom wall 27. The cross channel ironmembers 36 and 37 and the top plate 39 are sufficiently stiff so thatthe base structure 34 supports the entire Weight of the transformercasing without bowing or warping.

Means are interposed between the casing bottom wall 27 and the basestructure 34 for acoustically decoupling the casing bottom wall 27 fromthe rigid base structure. Preferably such acoustic decoupling meanscomprises means positioned between the casing bottom wall 27 and thebase structure for resiliently supporting the bottom Wall 27 out ofdirect contact with the base structure 34 so that the casing bottom wall27 can vibrate as a diaphragm without the strength or ability to forcethe casing side walls 28 into vibration. Such acoustic decoupling maycomprise isolating pads 41 of suitable resilient material such assynthetic rubber which raise the casing bottom wall 27 above andacoustically decouple it from the base structure 34. In the preferredembodiment of FIGS. 1-3 the isolating pads 41 rest upon the top plate 39and are spaced apart horizontally and arranged symmetrically relative tothe center of gravity of the core and coil assembly 20 so that theloading 'ofall of isolating pads 41 is approximately uniform. Relativelylarge isolating pads 41A are positionedbeneath the core feet 33approximately in vertical alignment with the core winding legs 12 andtransverse members 37 of the base structure and serve to acousticallyisolate the weight of the core and coil assembly 20 and the oil 22adjacent thereto from the base structure 34. Relatively small resilientpads 41B are positioned in spaced apart relation approximately below thepair of opposed tank side walls 28 longitudinal of the casing which.support external radiator tubes 44, and the resilient pads 41Bacoustically isolate from the rigid base structure 34 the weight of theremaining oil 22 and the weight of the casing 21 and the accessoriessuch as the radiator tubes 44 mounted on the casing. The resilientisolating pads 41A and 41B are spaced apart and arranged symmetricallyrelative to the center of gravity of the core and coil assembly 20 andcasing 21 so that the weight per unit area supported by all theresilient pads 41 is approximately uniform. Excessive loading orcompression of any one of the isolating pads 41 would permit a greatermagnitude of vibratory forces to be coupled to the base structure 34 atthe one pad than at the remaining isolating pads. A typical isolatingpad 4, 41 after loading by the weight of oil-filled casing 2 isapproximately one quarter inch in thickness, thus permitting therelatively thin bottom plate 27 to vibrate as a panel at the frequencyof the sound propagating force. Longitudinal and transverse serrationsmay be provided in the upper and lower surfaces respectively of theisolating pads 41 as shown in FIG. 5 to permit the material thereof toexpand horizontally when compressed by the weight of the core and coilassembly and the oil-filled casing.

FIG. 4 illustrates an embodiment of the invention wherein the casing andrigid base structure are not integral' and having means to releasablyafiix the casing 21 to the rigid base structure and to strengthen thecasing bottom wall 27 during shipment and handling of the oilfilledtransformer. The rigid base structure 34' does not have a top plate asin the embodiment of FIGS. 1-3 and comprises stiff channel iron members36 longitudinal of casing 21 crossed by stiff channel iron members 37'trans! verse thereto and disposed in approximately vertical alignmentbelow the core legs 12 and core feet 33. Plate members 42 and 43disposed beneath and welded to the longitudinal and transversestructural iron channels 36' and 37 form box section members for therigid base structure 34 of sufficient strength to withstand the forcesencountered when vacuum is drawn on casing 21. Resilient isolating pads41A and 41B are positioned between the casing bottom Wall 27 and thelongitudinal and transverse channel members 36 and 37 of the basestructure 34' in a manner similar to that described for the preferredembodiment, and the resilient pads are spaced apart horiozntally andarranged symmetrically relative to the center of gravity of the core andcoil assembly so that the loading of the isolating pads is substantiallyuniform. Means for releasably securing the casing 21 to the rigid basestructure 34' and for strengthening the casing bottom wall 27 mayinclude rigid internal metallic pads 48 welded to the interior surfaceof the casing bottom wall 27 and temporary bolts 49 protruding upwardlythrough clearance holes in the Web of channel members 36 and inresilient isolating pads 41C disposed between the base structure 34' andbottom wall 27 and releasably engaged within threaded apertures inbottom wall 27 extending into the rigid internal metallic pads 48. Thebolts 49 threadably engaging the rigid pads 48 temporarily afiix thecasing 21 to the rigid base structure 34' during shipment, processing,and handling of the transformer and strengthen the casing bottom wall 27so that it can Withstand the forces encountered when vacuum is drawn onthe casing 21. The temporary bolts 49 are removed at the permanentinstallation site.

The core and coil assembly 22 is acoustically decoupled from the rigidbase structure 34' principally by the isolating pads 41A whereas theweight of the oil 22 and the vibratory forces transmitted downwardly bythe oil are acoustically decoupled from the rigid base structure 34' bythe isolating pad means 41A, 41B and 41C.

The means for releasably securing the casing 21 to the rigid basestructure 34' during shipment may also include jacking lugs 52 welded tothe casing side walls 28'and positioned above portions 53 of the basestructure 34 extending beyond the casing side walls. Rigid shipping pads54 may be inserted between the casing bottom wall 27 and the rigid basestructure 34' prior to handling and shipment by raising the casing 21slightly using the jacking lugs 52. After the rigid shipping pads 54 arein position and the jacking meansremoved, the casing 21 may bereleasably clamped to the base'structure 34' by temporary bolts 55passing upwardly through clearance apertures in the extending portions53 of the rigid base structure 34' and releasably engaging threadedapertures in the jacking lugs 52. At the permanent installation site theoil-filled casing 21 is again raised slightly using the jacking lugs 52,and the rigid shipping pads 54, temporary bolts 55 and the jacking meansare removed, thereby per- 5 mitting the -weight of the oil-filled casing21 and thecore and coil assembly 20 contained therein to be supported onthe resilient isolating pad means 41 which acoustically decouple thecasing from the rigid base structure.

The present invention permits elimination of the resonant complianttubes lining the casing bottom wall when utilized with the transformersound reducing means disclosed in the copending application of CharlesC. Honey et al., Serial No. 781,163, filed Dec. 17, 1958, now U.S.Patent 3,102,246, and having the same assignee as this application.

In 'the embodiment illustrated in FIGS. 1-3 a hollow chamber is providedbetween the casing and the rigid base structure wherein the casingbottom Wall can vibrate as a panel to attenuate vibratory energy and thecasing is integral with the base structure but is acoustically decoupledtherefrom. Enclosure means is joined to the outer periphery of thecasing bottom wall 27 for forming alhollow chamber between the casingand the rigid base structure wherein the casing bottom wall vibrates asa panel 'to attenuate vibratory energy, and preferably such means issufficiently flexible so that it does not couple the casingto the basetsructure acoustically but is of suflicient strength to integrally unitecasing and base structure. Preferably such flexible enclosure meansincludes the peripherahflange 31 on the casing bottom wall 27 having itsouter margin 56 affixed in hermetically sealed relation to the outermargin on the top plate 39 of the rigid base structure 34. Thin metallicstrips 58 may be interposed between the outer margin 56 on flange 31 andthe top plate 39 around the entire peripherythereof and may be welded to.the flange 31 and to the top plate 39. The metallic strips 58 providethe spacing between tank bottom wall27 and top plate 39 required by theresilient isolating pads 41 which, in a typical transformer of theinvention, are approximately one quarter 4) inch thick when compressedby the weight of the casing 21 containing oil 22 and core and coilassembly 20. The rigid connection between flange 31 and top plate 39provided by the peripheral metallic strips 58 helps support the weightof the oil-filled casing 21 and integrally unites the casing 21 tothejrigid base structure 34. The fluid-tight joint provided theperipheral metal strips 58 between and welded to flange 31 and topplate39 seal the isolating pads 41 from theatrnosphere,.and the bottom wall27 together with the top plate 39sealed thereto define a hollow chamber60 positioned beneath the tank 21 wherein the bottom wall vibratesas apanel and which encloses the resilient supporting means 41 and aids inacoustically decoupling the rigid base structure 34 from the tank 21.

The tank bottom wall 27 is equal in thickness or thinner than the tankside walls 28 and acts in a manner analogous to a diaphragm and vibratesat an amplitude which will follow the vibrations originating in themagnetic core but does not possess suflicient rigidity and strength toforce the tank side walls 28 into vibration. The flange 31 on therelatively thin bottom wall 27 is of suflicient radial length andflexibility to substantially decouple the base structure 34 acousticallyfrom the casing "sidewalls 28, and satisfactory acoustic decouplingbetween casing side walls 28 and rigidbase structure 34 has beenobtained in'em'bodiments having flanges 31 extending approximately fourinches beyond the casing side walls 28. The weight "of the oil 22 andthe vibratory forces transmitted downwardly by the oil are acousticallyisolated 'frornthe rigid base structure by the flange 31 together withthe isolating pads 4 1A and 41B. It will be appreciated that thisembodiment .eliminates the necessity of the internal metallic pads 48,the shipping pads 54, and the temporary bolts 49 and 55 forstrengthening the casing bottom wall 27 and releasably securing thecasing 21 to the rigid base structure 34 as in the embodiment of FIG. 4.The hollow chamber 60 may be filled with air or with material having ahigh coefficient of sound absorption, one suitable material being lightdensity fiber glass.

In conventional stationary induction apparatus it 'is necessary -.tofirmly atfix the casing bottom wall to the rigid base structure so thatthe casing bottom wall can withstand the forces when a vacuum .is drawnon the casing. In the embodiment of FIGS. 1-3 the necessity of suchmeans for strengthening the casing bottom wall sufficiently to withstandthe forces involved when vacuum is drawn on the casing is obviated bymeans for equalizing the pressure on both sides of the-casing'bottomwall 27. Such pressure equalizing means maycomprise-means formaintaining the pressure in the chamber 60approximately equal to thepressure of the gas cushion .25above the oil 22, and preferably ametallic conduit 61 exterior of casing 21 at its lower end extendsthrough flange 31 and is in communication with chamber 60 and .at itsupper end extends through a side wall 28 of casing 21 and is incommunication with the gas 25. .It :will be.appreciated that conduit 61assures that .equal pressure is maintained on bothsides of bottom .wall27 when vacuum is drawn on casing 21, thus eliminating the necessity ofrigidly .aflixing the casing bottom vwall 27 .to the base structure 34'.

Although pressure equalizing conduit 61 is illustrated and described asregistering with gas cushion ,25, it .will be appreciated that theinvention is not so limited and comprehends other means for equalizingthe ,pressureon both sides of bottom plate 27, .for example, tubingregistering with chamber 60 and connected at its other end to anexpansion chamber maintained at the same pressure as the gas cushion 25.

Although the invention has been illustrated and described with spacedapart resilient isolatingpads 41 interposed between bottom wall 27 andtop plate 39, the improved results of the invention can also be'obtainedwith a single sheet of resilient material such as synthetic rubberinterposed between the rigid base structure34 and the casing bottom wallwhen .the elements of the core and coil assembly are symmetricallyarranged relative to the centerof gravity of the assembly and theaccessoriesare symmetrically arranged on the casing. Further, it willbe'apparent that flexible enclosure means other than the peripheralflange 56 can join the top plate 39 in sealing relation to the outermargin of the casing bottom wall 27 to form a hollow chamber beneath thecasing wherein the casing bottom wall 27 can vibrate as a diaphragm toattenuate vibratory energy without coupling the casing to the basestructure acoustically. A

While there have been shown and describedparticular embodimentsof theinvention, it will beobvious tothose skilled in'the art that variouschanges and modifications can be made therein without'departing from theinvention and, therefore it is intended in the appended'claims to coverall such changes and modifications which fall within the true spirit andscope of the invention.

What we claim as new and desire'to secure by Letters Patent of theUnited States is:

1. In stationary induction apparatus, in combination, a casing having abottomwall and pairs of opposed side walls, dielectric liquid withinsaid casing, a core andcoil assembly immersed :in said liquid withinsaidicasing'and havng a plurality of feet resting upon said bottomcasing wall and arranged symmetrically relative to the centerzof gravityof said assembly, a rigid base structure beneath said bottom wall, aplurality of flat isolating pad means of resilient material havingsubstantial,horizontaldimensions interposed between said bottom wall andsaid base structure for resiliently supporting said casing out of directcontact with said base structure'so .that said-bottom wall can vibrateas apanel under the vibratory forces originating in said core, certain'of said resilient supporting means being positioned beneath said feetand others being-positioned belowieach side wall of one pair of saidopposed casing sidewalls, said resilient supporting means being spacedapart and the loading thereof resulting from the weight of saidliquid-filled casing being approximately uniform.

2. In an electrical transformer, in combination, a tank having a bottomwall and side walls at least as thick as said bottom wall, dielectricliquid Within said tank, a transformer core and coil assembly includinga magnetic core having winding legs linked by electrical coils immersedin said liquid within said tank and Supported upon said bottom wall, arigid base structure beneath said tank bottom wall, flat isolating padmeans of resilient material interposed between said tank bottom wall andsaid base structure for resiliently supporting said tank bottom wallabove said base structure so that said bottom wall can vibrate as apanel and does not rigidly couple to said tank side walls through saidbase structure the vibratory forces originating in said core andtransmitted downwardly by said liquid dielectric, and means releasableexternally of said tank for rigidly connecting said tank to saidbase'structure during shipping and handling of said transformer, saidconnecting means including rigid pads secured in sealing relation to theinner surface of said tank bottom wall and positioned above said basestructure, said tank bottom wall having threaded apertures extendinginto said rigid pads and being accessible from the exterior of saidtank, said rigid pads strengthening said bottom wall against the forcesresulting from vacuum within said tank.

3. In an electrical transformer, in combination, a tank having sidewalls and a bottom wall, dielectric liquid within said tank, atransformer core and coil assembly immersed in said liquid within saidtank and supported upon said tank bottom wall, a rigid base structurebeneath said tank bottom wall having portions extending beyond said tankside walls, a plurality of flat isolating pad means of resilientmaterial interposed between said bottom wall and said base structure forresiliently supporting said tank out of direct contact with said basestructure so that said bottom wall can vibrate as a panel under thevibratory forces originating in the transformer core and transmitteddownwardly by said dielectric liquid and does not rigidly transmit saidvibratory forces to the side walls" of said tank through said basestructure, said isolating pad means being spaced apart and the loadingthereof by the Weight of said tank being approximately uniform, andmeans including jacking lugs on the side walls of said tank disposedabove said extending portions of said base structure for rigidlyconnecting said tank to said base structure during shipment and handlingof 'said' transformer, said jacking lugs permitting raising of said tankrelative to said base structure and the insertion of rigid membersbetween said tank bottom wall and said base structure during shipmentand handling of said transformer, said last-named means includingreleasable bolt meansfor securing said jacking lugs to said extendingportions of said base structure.

4. In stationary induction apparatus, in combination, a casing having abottom wall and pairs of opposed side walls, dielectric liquid withinsaid casing, a core and coil assembly immersed in said liquid withinsaid casing resting upon said bottom wall, said assembly including amagnetic core having a plurality of core legs, a plurality of crossedlongitudinal and transverse structural iron members forming a rigid basestructure and having a top plate disposed beneath said bottom wall, saidlongitudinal members being positioned approximately below one pair ofsaid opposed sidewalls and said transverse members being disposed belowlegs of said core and arranged symmetrically relative to the center ofgravity'of said assembly, and a plurality of flat isolating pad means ofresilient material interposed between said bottom wall and said topplate of said base structure for resiliently supporting said casing outof contact with said base structure so that said bottom wall can vibrateas a panel, certain of said isolating pad means being positioned belowsaid core legs and others being disposed below said one pair of casingside walls and said isolating pad means being spaced apart and theloading therer 8 of by the weight of said liquid-filled casing beingapproximately uniform.

5. In an electrical transformer, in combination, a tank having pairs ofopposed side Walls and a bottom wall extending in a peripheral flangebeyond said side walls, said bottom wall being at least as thick as saidside walls, dielectric liquid within said tank, a transformer core andcoil assembly including a magnetic core having a plurality of windinglegs linked by electrical coils and a plurality of feet positionedsymmetrically relative to the center of gravity of said assembly restingupon said tank bottom wall, a rigid base structure beneath said tankbottom wall including a top plate substantially coextensive with saidtank bottom wall, a plurality of flat isolating pad means of resilientmaterial interposed between said tank bottom wall and said top plate forresiliently supporting said tank bottom wall out of contact with saidtop plate so that said tank bottom wall can vibrate as a panel, certainof said isolating pad means being disposed below said feet and othersbeing disposed beneath each of one pair of said opposed tank side walls,means for connecting the outer marginson said flange and said top platein sealing relation, said bottom wall so connected to said top platedefining a hollow chamber beneath said tank wherein said tank bottom'wall can vibrate as a panel to attenuate vibratory energy and enclosingsaid isolating pad means and sealing them from the atmosphere, saidflange extending radially beyond said side walls and substantiallyacoustically decoupling said tank from said rigid base structure.

6. In stationary induction apparatus, in combination, a tank having sidewalls and a bottom wall extending in a peripheral flange beyond saidside walls, dielectric liquid within said tank, a core and coil assemblyincluding a magnetic core linked by an electrical coil immersed in saidliquid within said tank and supported upon said tank bottom wall, arigid base structure beneath said tank bottom wall including a top platesubstantially coextensive with said tank bottom wall, flat isolating padmeans of resilient material interposed between said tank bottom wall andsaid top plate for resiliently supporting said tank bottom wall out ofdirect-contact with said base structure so that said tank bottom wallcan vibrate as a panel and does not rigidly transmit to said tank sidewalls the vibratory forces originating in said magnetic core andtransmitted downwardly by said liquid dielectric, and means forconnecting the outer margin. on said flange in sealing relation to saidtop plate, said bottom Wall and said top plate sealed thereto defining ahollow chamber beneath said tank wherein said bottom wall can vibrate asa panel to attenuate said vibratory forces and enclosing said isolatingpad supporting means and sealing them from the atmosphere, said flangeso connected to said top plate substantially decoupling said bottom wallacoustically from said rigid base structure.

7. In stationary induction apparatus in accordance with claim 6including conduit means communicating with the interior of said chamberand maintaining the pressure within said chamber approximately equal tothe internal pressure within said tank.

8. In an electrical transformer, in combination, a tank having sidewalls and a bottom wall extending in a peripheral flange beyond saidside walls, dielectric liquid 'within said tank, a transformer core andcoil assembly immersed in said liquid within said tank and supportedupon said tank bottom wall, a rigid base structure having a top platebeneath said tank bottom wall, flat means of resilient materialinterposed between said tank bottom wall and said top plate forresiliently supporting said tank bottom wall out of contact with saidbase structure so that said bottom wall can vibrate as a panel and doesnot rigidly transmit to said base structure the vibrations originatingin the transformer core and transmitted downwardly by said liquiddielectric, and means including said peripheral flange for connectingsaid top plate to said tank bottom wall around the entire outer marginthereof and for substantially decoupling said tank acoustically fromsaid base structure, said connecting means together with said top plateand said tank bottom wall defining a chamber beneath said tank whereinsaid bottom wall can vibrate as a panel to attenuate said vibrations andsurrounding said resilient supporting means and sealing them from theatmosphere.

9. In an electrical transformer, in combination, a casing having abottom wall and side walls at least as thick as said bottom wall andsaid bottom wall extending in a peripheral flange beyond said sidewalls, dielectric liquid within said casing, a transformer core and coilassembly immersed in said liquid dielectric within said casing andsupporting on said bottom wall, a gas cushion within said casing abovesaid liquid dielectric, a rigid base structure beneath said bottom wallincluding a top plate substantially coextensive with said tank bottomwall, means interposed between said bottom wall and said top plate forresiliently supporting said bottom wall out of contact with said topplate so that said bottom wall can vibrate as a panel, the outer marginsof said flange and said top plate being joined in sealing relation, saidbottom wall and said top plate so sealed together defining a hollowchamber beneath said casing wherein said bottom wall can vibrate as apanel to attenuate vibratory energy and enclosing said resilientsupporting means and sealing them from the atmosphere, and meansincluding a conduit communicating with the interior of said soundabsorbing chamber for maintaining the pressure within said chamberapproximately equal to the pressure of said gas cushion.

10. In an electrical transformer, in combination, a tank having sidewalls and a bottom wall extending in a peripheral flange beyond saidside walls, liquid dielectric within said tank, a transformer core andcoil assembly immersed in said liquid within said tank and having aplurality of feet symmetrically arranged relative to the center ofgravity of said assembly resting upon said tank bottom wall, a rigidbase structure beneath said tank bottom Wall including a top platesubstantially coextensive with said bottom wall, a plurality of flatisolating pad means of resilient material interposed beneath said bottomwall and said top plate for resiliently supporting said tank bottom wallout of contact with said base structure so that tank bottom wall canvibrate as a panel and does not rigidly couple to said tank side wallsthe vibratory forces originating in said core and transmitted downwardlyby said liquid dielectric, certain of said isolating pad means beingdisposed beneath said feet, said isolating pad means being spaced apartand the loading thereof resulting from the weight of said tank beingapproximately uniform, the outer margin of said flange being joined insealing relationship to said top plate, said bottom wall and said topplate joined thereto defining a hollow chamber beneath said tank whereinsaid bottom wall can vibrate as a panel to attenuate said vibratoryforces and enclosing said isolating pad means and sealing them from theatmosphere.

11. An electrical transformer comprising, in combination, a tank havingside walls and a bottom wall extending in a peripheral flange beyondsaid side walls, dielectric liquid within said tank, a transformer coreand coil assembly immersed in said liquid within said tank and supportedupon said tank bottom wall, a rigid base structure beneath said tankbottom wall having a top plate substantially coextensive with saidbottom wall, flat isolating pad means of resilient material interposedbetween said tank bottom wall and said base structure for resilientlysupporting said bottom wall above said base structure so that saidbottom wall can vibrate as a panel and does not couple to said tank sidewall the vibratory forces originating in said core and transmitteddownwardly by said liquid dielectric, metallic strip means interposedbetween said top plate and said bottom wall and welded thereto aroundthe outer margin of said flange and joining said top plate in sealingrelation to said bottom wall, said top plate so joined to said bottomWall defining a hollow chamber between said tank and said base structurewherein said bottom wall can vibrate as a panel to attenuate saidvibratory forces and enclosing said isolating pad means and sealing themfrom the atmosphere.

12. In an electrical transformer, in combination, a tank having a bottomwall and side walls at least as thick as said bottom wall and saidbottom wall extending in a peripheral flange beyond said side Walls,dielectric liquid within said tank, a transformer core and coil assemblyincluding a magnetic core linked by an electrical coil immersed in saidliquid within said tank and supported upon said tank bottom wall, arigid base structure beneath said tank bottom wall including a top platesubstantially coextensive with said tank bottom wall, flat isolating padmeans of resilient material interposed between said tank bottom wall andsaid top plate for resiliently supporting said tank bottom wall out ofdirect contact with said top plate so that said bottom wall can vibrateas a diaphragm, said resilient supporting means being spaced apartsymmetrically relative to the center of gravity of said core and coilassembly and the loading thereof, resulting from the weight of said tankcontaining said core and coil assembly and said dielectric beingsubstantially uniform, and means for connecting the outer margins onsaid flange and said top plate in sealing relation, said bottom wall soconnected to said top plate defining a hollow chamber beneath said tankwherein said bottom wall can vibrate as a diaphragm to attenuatevibratory energy and enclosing said supporting means and sealing saidmeans from the atmosphere, said flange extending radially beyond saidtank side walls and substantially acoustically decoupling said tank fromsaid rigid base structure.

References Cited by the Examiner UNITED STATES PATENTS 1,846,887 2/1932Matthews 336- 2,734,096 2/1956 Ennis 336100 2,864,065 12/1958 Horelicket a1. 336-100 2,870,858 1/1959 Adams 336-100 3,102,246 8/1963 Honey etal 336100 3,125,735 3/1964 Twomey 336100 X 3,125,736 3/1964 Aronson336100 KATHLEEN H. CLAFFY, Primary Examiner.

E. JAMES SAX, JOHN F. BURNS, LARAMIE E. AS-

KlN, Examiners.

M. W. COOK, S. H. BOYER, J. I. BOSCO,

Assistant Examiners.

1. IN STATIONARY INDUCTION APPARATUS, IN COMBINATION, A CASING HAVING ABOTTOM WALL AND PAIRS OF OPPOSED SIDE WALLS, DIELECTRIC LIQUID WITHINSAID CASING, A CORE AND COIL ASSEMBLY IMMERSED IN SAID LIQUID WITHINSAID CASING AND HAVING A PLURALITY OF FEET RESTING UPON SAID BOTTOMCASING WALL AND ARRANGED SYMMETRICALLY RELATIVE TO THE CENTER OF GRAVITYOF SAID ASSEMBLY, A RIGID BASE STRUCTURE BENEATH SAID BOTTOM WALL, APLURALITY OF FLAT ISOLATING PAD MEANS OF RESILIENT MATERIAL HAVINGSUBSTANTIALLY HORIZONTAL DIMENSIONS INTERPOSED BETWEEN SAID BOTTOM WALLAND SAID BASE STRUCTURE FOR RESILIENTLY SUPPORTING SAID CASING OUT OFDIRECT CONTACT WITH SAID BASE STRUCTURE SO THAT SAID BOTTOM WALL CANVIBRATE AS A PANEL UNDER VIBRATORY FORCES ORIGINATING IN SAID CORE,CERTAIN OF SAID RESILIENT SUPPORTING MEANS BEING POSITIONED BENEATH SAIDFEET AND OTHERS BEING POSITIONED BELOW EACH SIDE WALL OF ONE PAIR OFSAID OPPOSED CASING SIDEWALLS, SAID RESILIENT SUPPORTING MEANS BEINGSPACED APART AND THE LOADING THEREOF RESULTING FROM THE WEIGHT OF SAIDLIQUID-FILLED CASING BEING APPROXIMATELY UNIFORM.